Device for crucible-free zone melting



June 15, 1965 R. EMEIS &

DEVICE FOR CRUCIBLE-FREE ZONE MELTING Filed July 28, 1959 v 3Sheets-Sheet 1 June 15, 1965 R. EMEIS DEVICE FOR CRUCIBLE-FREE ZONEMELTING 5 SheetS-Shet 3 Filed July 28, 1959 United States Parent ODEVICE FOR CRUClBLE-FREE ZONE MELTING Reimer Emeis, Ebermannstadt, UpperFranconia, Germany, assignor to Siemens-SchuckertwerkeAktiengesellschaft, Erlangen, Germany, a corporation of Germany FiledJuly 28, 1959, Ser. No. 830,()26 Claims priority, application Germany,July 30, 1958, S 59,210 4 Claims. (Cl. 23--273) My invention relates toa device for crucible-free zonemelting of semiconductor rods,particularly silicon rods, within a metallic high-vacuum vessel in whichthe semiconductor rod is held vertically at both ends while beingsubjected to zone-melting with the aid of a ring-shaped heatersurounding the rod and traveling longitudinally along the rod. r

In a known device for crucible-free zone melting in high vacuum, thesemiconductor rod and the zone heating device are accommodated inside ametal bell of relatively large horizontal inner width which isvac'uum-tightly seated upon a base plate. The 'supports and otherdevices for holding the rod and the heater are mounted on the baseplate, and all bushings and shaft seals required for driving therod-holding devices and for shifting the zone heater along the rod arelocated on or in the base plate. The exhaust duct for connecting avacuum source to the processing chamber is likewise mounted on the baseplate. This involves the difi'iculty that foreign particles or materialvaporized from the rod may drop into the exhaust duct and may reach thevacuum pump. Another difiiculty is the fact that the above-mentioredparts, all mounted on the base plate, impose a severe limitation uponthe diametrical size of the duct opening so that a relatively longperiod of time is needed, when starting the operation, for producing thehigh vacuum. Furthermore, for exchanging a semiconductor rod orservicing the auxiliary devices within the chamber, the bell must belifted of the base plate by a hoisting device.

It is an object of my invention to eliminate the abovementionedshortcomings and limitation of crucible-free zone melting devices and toprovide a processing apparatus which can more readily be serviced,afiords better protection of the vacuum producing equipment, and greatlyreduces the starting-up time required for reducing the pressure in theprocessing chamber to the required high vacuum.

According to my invention, a vacuum device for crucble-free zone meltingof semiconductor rods is provided With a metal housing whose interierforms the/high- Vacuum chamber and which is vertically elongated and hasits bottom and top irremovably joined or integral with the vertical sidewalls. Furthermore, one of the two clamps or other holders for attachingthe ends of the semiconductor rod is mounted on the bottom, and theother is mounted on the top of the housing so that the housing itselfforms the supporting structure for the top holder. The vacuum chamber inthe housing is accessible for servicing through a lateral, sealableopening, and another lateral opening in one of the side walls isprovided for connection of the device to the high-vacuum pumpingequipment, the latter opening being located in vertically spacedrelation from the bottom surface of the housing.,

According to another, preferred feature of my invention, the vacuumhousing is given prismatic shape and a preferably rectangular horizontalcross section, and one of the vertical side walls is provided with asealable closure device in form of a hinged door. Another one of theside walls is provided with the exhaust opening and duct for connectionto the vacuum pump. Another connection for a pre-vacuum pump, ifdesired, may be provided on the remaining vertical side wall of thehousing.

By vrtue of the above-mentioned features, the diameter of the exhaustopening for producing the high vacuum within the processing chamber isnot limited by the presence of the other Components, nor is the interiorobstructed by any supports for the upper rod holder, and the entireinterior of the device is more readily accessible for servicing than isthe case in the above-mentioned devices heretofore available.

The foregoing and more specific objects, advantages and features of myinvention will be apparent from, and will be described in, the followingwith reference to the embodiment of a processing device according to theinvention illustrated by way of example on the accompanying drawings inwhich: i

FIG. 1 is a part sectional and perspective View of the device connectedwith evacuating equipment.

FIG. 2 illustrates the same device in a vertical section taken along theline II-II in FIG. 3, the view being from the door side of the device.

FIG. 3 is a sectional top View of the device, the section being takenalong the line III -III indicated in FIG. 2.

The housing 2 of the illustrated device has generally the shape of avertically elongated prism of rectangular or approximately square crosssection. The front wall of the housing is formed by a closure plate 3which forms a door. The walls of the housing as well as the door arepreferably provided with cooling means consisting, for example, ofcopper tubing (not illustrated) soldered to the walls and door in orderto pass a flow of cooling water through the tubing during operation ofthe device. An inspection window 30 extends approximately over theentire length of the semiconductor rod to be processed and permitsobserving the zone-melting operation. A duct 4 for'connection to avacuum pumping device 5 is mounted on the rear wall of the housing andcommunicates with the interior of the housing through an opening ia oflarge diameter extending over the predominant portion of the horizontalhousing width. The opening 4a and the exhaust duct 4 are located abovethe bottom surface of the vacuum chamber so that any particles orsubstances dropping onto the bottom of the device cannot enter into thevacuum equipment. r v

The semiconductor rod 6, for example of silicon, is mounted in theprocessing chamber by means of two holders 7 and 7a. The two-holders,shown to consist of respective chucks with clamping screws 7b, aremounted in Vertical coaxial alignment on respective coaxial shafts 8 andSa which pass through respective vacuum-tight sealng bushings 8b and 8cof the housing bottom and top to the outside where they are connectedwith driving and control devices (not shown) which permit displacing theholders longitudinally and/or imparting rotationthereto. i

v The device is further provided with a ring-shaped zone heaterconsisting of a fiat induction coil 11 mounted on terminal blocks 12 ofa shifting device 13 which permits moving the axially narrow heater 11vertically along the rod 6 in order to mel-t a correspondingly narrowzone of the rod and to displace the molten zone gradually along the rodaxis. A semi-cylindrical shield 14 of sheet metal protects the device 13from heat radiation coming from the molten zone and also from depositionof evaporated material.

The heater and the shifting device are mounted along one of the cornerareas of the prisma-tic processing chamber. As best apparent from FIG. 2the device 13 comprises several concentric tubes which are separatedfrom each other by evacuated interspaces and also serve for supplyingthe electric current to the terminal blocks 12 of the heater coil 11.The coil 11 consists of a copper tube which forms part of a coolantcirculation system. The coolant passes from the outsideof the housingthrough i the inner tubila'r portion 1341, thence through one of the I-hollow blocks 12, the tubular coil'll, the other block 12, "and throughthe cylindr'ical interspace aroundthe tube 13:; back to the outside ofthe processing device.

The 'heat shield 14 isfastenedto the top and bottom of -thevacuumhousing b'y screws and may be provided with water cooling, for;example, with' the aid of'copper 't'ubing (not shown) soldered to theshield'14.

I A gripper device, comprising two vertical "ishaf ts 18. and 18.',- ismounted 'along another edge of' the prisr'naticprecessing chamber,preferably, and as shown, near one ;of thetwo edges remote from thedoor.As is best ap: v

parent from FIG. 3 two grippers 15 and 1541 are fastened %hys-means ofset screws to the respective vertical sh-afts 18 and 18z,' the twogrippe rs being longitudinally' diplace- Q able s o that-they canbeSecured in any desired height.

The shaftss and 1841 carry respective spur gears 15 and 19a which arein'mesh with each other and are driven hy a spur gear 2!) whose shaft zaextends through a rotational 'sealflto the outside where it is actuatedby a worm ge'ar; 31 and worm 32 preferably of the self-looking type. Forprotecting the semiconductor rod 6 from being contaminatedflhe ends ofthe grippers '15, lsa are provided i iThehorizontal spacing of theobservation window from the vertical axis of the'rod holders 7,7z,'ispreferablyat least five times the immerdiameter of the ring-shapedheater coil 11 in order to prevent the deposition, forming itself on theinside of the observation window due to mat'erial evaporating from therod, from becoming so dense as to inter-f re with proper observationwithin too short i I a processing time. t rnines the locations atwhichshafts' and Sa, and the' The* just-ment-ioned spac ingdeterappertaining vacuum-tight `seals ;bottom of the housing z.

V remaining front corners of the vacuum chamber. Such withtubular piecesl ofheat-resistant and wear-resista nt-material,preferablyrqua-rtz., v i

The grippen'device facilitates servicing and afiords eliminating one ormore operatingsteps, such a-s open- ;ing and closing of the door,inserting a semiconductor rod and evacuating the housing, thus saving aconsiderable amount of time, for example in a casewhere the rod 6 properis to be inserted'between two rod pieces' of c'rystal seedspreviouslyfastened in the respective holders 7 and '7a, and is-then to be fusedtogether with ft-hese seed pieces. 5 For such operation the rod piecesor seeds can be clamped in the holders and the rod proper can befastened in'the grippendevice when the door is openl and the zonemelting devce, is being 'set up for operation. Then'the; door can beenclosed and the housing evaporated, whereafterthefusing operationrequired for ;oinin'g the'rod 6 with, the end pieces or'seeds can be ef-,40 jfected with the aid of heater coil 11, and the zone melt-.ing-'proper can'be carried'out without requiring renewed" J `{openingof the doo-r or renewed evacuation of the processingclz aniben I i fl-Asshownirf-FIG. 3 the door-like closure plate 3 cari ;ries' a rubbergask-et zs'which is seated in a swallow-tail 'j gr oove orotherwisefastened to the door. The door is jjoined with the -housing bydouble-type hinges 2-1 whose ;two hnge axes 'are approxim'ately locatedin theplan'e of the doorwhenthe door is' closedand tightened. i This,aifords obtaining a vacuum tight sealingof the door under 'the'etfect'of the ambient pressure-without encountering' l-ateral -displacement ofthe'door as a consequence of prese i sure changes. The door is providedwi-t-ha handle 29; 3 L The observation'windcw 30 is, covered by a hardglass pane 23 ofsufficient thickness to withstand all occurring i pressures. The pane 23 is vacuum-tightlysealedby means a of a 'gasket 22preferably of rubber An exterior protective sheet' Z'f of transparentand splinter-proof glass plasfltc', or'glassplastic'compositiom ismounted on spacer tubes 26 at some distance from the hard-gl ass pane23,

jleaving an int'erspce preferably ahout equal to thethickness ofgpanez.Theprotective sheet 27 consists preferably; of;` polymethylmetharylateknown under the `trade j %name Plexiglas. For protecting the hard-glasspane 23 fronibeng `-`soiled by evaporated material, another thinnerglass pane 24 is removably inserted on the inner' side of -a trap may bemounted on the top of the housing 2 so as to' suspend therefrom. Thetrap tube, 'being closed' at the 'bottom toward the interior off theprocessing charnber, may have its upper, open end passingvacuum-tightly' :through the top of the housing ,so 'that it can befilled from the outside with coolant, for example liquid air.

' 'It will'be obvious to those skilled in the art, upon study- 'ing thedisclosure, that iny invention permits'ofjvarious modications' withrespect' to design-and arrangen entof the device Components and hencemay be emb odied in apparatus other than particularly statedvanddescribed herein, without departing from the essential features of niy iinvention and within the scope of the claims annexed' hereto. A

I claim; i i i 1. A device for crucible-free zone melting of silicon Vand other semiconductor rods, comprising a' stationary metal housing ofgenerally pr isrnatic and verticallyelom i gated shape forming a vacuum,charnber 'and ,having fectangular vertical side walls and respectivehorizontal-- top and ,bottom parts'irrernovably 'joined with said Walls,two serniconductor-rod holders mounted on'sa'd respective 'top andbottom parts .in vertical and coa rial' alig i ment on an axissubstantially coinci'dent with the vertical r center axis of said'housing for .holding therespective ends of theirod to be processed, aring-shap'ed'induction r heater surrounding the vertical rod-'holderaxis and being displaceable in the axial direction, the vertical frontwall I i' of said housing having an accessiopening for servicingsaidchamben said access opening havingaheight equal to at least themajor part of the maximumaxial displace-i` i ment of said heater aclosure meinber'pivotally mounted -on 'said housing in front of saidfront wall to close said access' opening and scaling meansbetween saidhousing 'and said closure member, saidclosure' member having j anobservation window extendng verticallyover a major` part of the heightof said access opening, and comprising ,v a transparent:pressure-withstanding o'ter pane and a I removably mounted inner pane'to protect said.: outer' pane from, soilage, said housing having anevacuating opening in the vertical reanwall and having an evacuating;duet communicating .through i said 'opening with' said chamber, ;saidlatteropening having a width substantially equal 'to that of saidchamber and being upwardly-spaced from said bottom part, the lower oneof said rod holders being vertically displaceable, two rod-shapeddrive'means' for axially displacing said one rod holder and said heate'respectivelY said respective drive meansextending' r through saidhousing bottom parttQi -'the outside,-and

?the door. Theau xiliary pane '23 is held'by means of a( i 'spredingspring 2 5 so that-it can re'adily-be removed, or rexchahged-forcleaning,purposes- The inner pane 24 may also'be attachedby other means, suchas" by one or &more leafsprirgsattached by screws-tothe dooL For protecting the observer@ eyesight, the sheet-27 may-begiven a dark coloring so that no protective goggles are needed foobservingthe melting operation; i

said.rod-shaped jdrive means -for said heater extending t verticallybetween said center axis and one of the verticalrear edges ofsaidhousing 2. In a device for-crucible-freefzone meltng of :neltablerod, `a 'stationaryjhou'sing two holder members in the` housing,means-for relatively displacing the,holder: memberstivertically withrespect toeach other, a 'meltf ing coil in .thejhousing means forsupportingahd for 'relatively displacingfthe coilvertically oftheveni-cel' t aXis of the holder membersj' the improvement thereing thehousing V having i an 'access opening having a 'height' substantially atleast as great .as'the entire vertical' displa'cement path of 'themeltir g; coil, and a closure mem- A tubular cooling trap may be rnounted' in one of the ber for said opening having an observation windoweX- tending over at least the major part of the height of the opening,and two rod-gripping devices in said housing, each including a rotaryvertical shaft and a gripper means mounted on the shaft, and meansextending through the housing to turn the shats to position the gripperson opposite sides of the rod to hold the rod, so that upon opening theclosure member the rod can be placed and held between the holders at thestart of the melting operation, and, after closing the closure memberand commencing the melting, the grippers can be turned away from the rodto permit the said relative displacement of the melting coil.

3. A device for crucible-free zone melting of silicon and othersemiconductor rods, comprising a stationary metal housing of verticallyelongated shape forming a vacuum chamber and having vertical side Wallsand having a top and a bottom irremovably joined with said side walls,two semiconductor-rod holders mounted on said top and said bottomrespectively in vertical and coaXial alignment for holding therespective ends of the rod to be processed, the axis of said holdersbeing substantially coincident with the vertical center axis of saidhousing, a ring-shaped induction heater surrounding said rod-holder aXisand being displaceable along said axis a distance constituting a majorportion of the height of said chamber, vertically displaceable means insaid chamber for supporting and moving said heater along said distancethe vertical front wall of said housing having an access openingextending vertically fxom one of said holders to the other for servicingsaid chamber, a sealable closure plate covering said access openingduring zone-melting operation and having a Vertically elongatedobservation window eXtending over substantially the entire verticaldisplacement path of said induction heater, said cover plate beinghinged to said housing and having a vertical hinge aXis for openingmovement of said plate in the outward direction away from said accessopening, said housing having an evacuatng opening located in thevertical rear wall and having a diameter substantially equal to thewidth of said chamber, said housing having an evacuating ductcommunicating through said latter opening with said chamber, and saidmeans for supportin said he-ater extending vertically in the rearportion of said chamber so as to be located behind said rod holdersrelative to said access opening.

4. In a Zone-melting device according to claim 3, said housing havingthe shape of a Vertically elongated prism with rectangular crosssection, said closure plate having substantially the same size as saidvertical front wall of said housing, and said heater supporting meansextending through said bottom part to the outside of said housing andalong a rear vertical edge of said chamber at a place substantiallybetween said rear edge and said rod-holder axs.

References Cited by the Examiner UNITED STATES PATENTS 2,745,13 1 5/56Auwarter.

2,870,309 1/59 Capita 23-301 2,876,147 3/59 Kniepkamp 23-30l 2,902,3509/59 i Jenny 23 301 2,904,663 9/ 59 Emeis et al 23-273 2,972,525 2/ 61Emeis.

OTHER REFERENCES Buehler Rev. Scient Inst., Vol. 28 (June 1957), pages453-460, Q/184/RS.

Keck Review of Scient. Inst., Vol. 25, No. 4, pp. 331- 334, April 1954.

Marshall et al.: Journal of Scientic Instruments, Vol. 35, April 1958,pp. 121-125.

NORMAN YUDKOF-F, Pr'mary Examiner.

MAURICE A. BRINDISI, GEORGE D. MITCHELL,

Exam'ners.

2. IN A DEVICE FOR CRUCIBLE-FREE ZONE MELTING OF A MELTABLE ROD, A STATIONARY HOUSING, TWO HOLDER MEMBERS IN THE HOUSING, MEANS FOR RELATIELY DISPLACING THE HOLDER MEMBERS VERTICALLY WITH RESPECT TO EACH OTHER, A MELTING COIL IN THE HOUSING, MEANS FOR SUPPORTING AND FOR RELATIVELY DISPLACING THE COIL VERTICALLY OF THE VERTICAL AXIS OF THE HOLDER MEMBERS; THE IMPROVEMENT THEREIN, THE HOUSING HAVING AN ACCESS OPENING HAVING A HEIGHT SUBSTANTIALLY AT LEAST AS GREAT AS THE ENTIRE VERTICAL DISPLACEMENT PATH OF THE MELTING COIL, AND A CLOSURE MEMBER FOR SAID OPENING HAVING AN OBSERVATION WINDOW EXTENDING OVER AT LEAST THE MAJOR PART OF THE HEIGHT OF THE OPENING, AND TWO ROD-GRIPPING DEVICES IN SAID HOUSING, EACH INCLUDING A ROTARY VERTICAL SHAFT AND A GRIPPER MEANS MOUNTED ON THE SHAFT, AND MEANS EXTENDING THROUGH THE HOUSING TO TURN THE SHAFTS TO POSITION THE GRIPPERS ON OPPOSITE SIDES OF THE ROD TO HOLD THE ROD, SO THAT UPON OPENING THE CLOSURE MEMBER THE ROD CAN BE PLACED AND HELD BETWEEN THE HOLDERS AT THE START OF THE MELTING OPERATION, AND, AFTER CLOSING THE CLOSURE MEMBER AND COMMENCING THE MELTING, THE GRIPPERS CAN BE TURNED AWAY FROM THE ROD TO PERMIT THE SAID RELATIVE DISPLACEMENT OF THE MELTING COIL. 